The use of polyalpha-olefins or copolymers thereof to reduce the drag of a hydrocarbon flowing through a conduit, and hence the energy requirements for such fluid hydrocarbon transportation, is well known. These drag reducing agents, or DRAs, have taken various forms in the past, including slurries or dispersions of ground polymers to form free-flowing and pumpable mixtures in liquid media. A problem frequently experienced with simply grinding the polyalpha-olefins (PAOs), however, is that the particles will “cold flow” or stick together after the passage of time, thus making it impossible to place the PAO in the hydrocarbon where drag is to be reduced in a form of suitable surface area, i.e., particle size, that will dissolve or otherwise mix with the hydrocarbon in an efficient and effective manner. Further, the grinding process or mechanical work employed in size reduction often degrades the polymer, thereby reducing its drag reduction efficiency.
One common approach to preventing or reducing cold flow problems is to coat the ground polymer particles with an anti-agglomerating or partitioning agent. Cryogenic grinding of the polymers to produce the particles prior to or simultaneously with coating with an anti-agglomerating agent has also been used. However, some powdered or particulate DRA slurries require special equipment for preparation, stable storage and injection into a conduit to ensure that the DRA is completely and effectively dissolved in the hydrocarbon stream.
Gel or solution DRAs (those polymers essentially being in a viscous solution with hydrocarbon solvent) have also been tried in the past. However, these drag reducing gels also demand specialized injection equipment, as well as pressurized delivery systems. The gel or solution DRAs are relatively stable and have a defined set of conditions that must be met by mechanical equipment to pump them, including, but not necessarily limited to, their viscosity, vapor pressure, shear properties, and the like. The gel or solution DRAs are also limited to about 10 percent by weight polymer as a maximum concentration in a carrier fluid due to their typical high solution viscosity. Thus, transportation costs for these DRAs are often considerable and prohibitive, since up to about 90 percent of the volume being transported and handled is inert material.
U.S. Pat. No. 2,879,173 describes a process for preparing free-flowing pellets of polychloroprene that involves suspending drops of an aqueous dispersion of the polychloroprene in a volatile, water-immiscible organic liquid in which the polymer is insoluble at temperatures below −20° C. Once the drops are completely frozen and the polychloroprene coagulated, the frozen pellets are separated from the suspending liquid and coated, while still frozen, with from 5 percent to 20 percent of their dry weight of a powder which does not react with the polychloroprene under normal atmospheric conditions. Finally, the water and any adhering organic liquid are removed via vaporization effected by warming the pellets.
U.S. Pat. No. 3,351,601 describes a method for coating pellets of a normally sticky thermoplastic binder material by using a mixture of a minor proportion of a vinyl chloride/vinyl acetate copolymer and a major proportion of a chlorinated paraffin wax with powdered limestone or talc powder.
U.S. Pat. No. 3,528,841 describes the use of microfine polyolefin powders as parting agents to reduce the tackiness of polymer pellets, particularly vinyl acetate polymers and vinyl acetate copolymers.
Canadian patent 675,522 discloses a process of comminuting elastomeric material for the production of small particles. The process includes presenting a large piece of elastomeric material to a comminuting device, feeding powdered resinous polyolefin into the device, comminuting the elastomeric material in the presence of the powdered polyolefin, and recovering the comminuted elastomeric material.
U.S. Pat. No. 3,884,252 discloses a process for reducing oxidative degradation and cold flow of polymer crumb by immersing the crumb in a non-solvent such as water, and/or dusting the crumb with a powder such as calcium carbonate and 2,6-di-t-butylparacresol, 4,4′-methylene-bis-(2,6-di-t-butylphenol) or another antioxidant. That patent also mentions a process for reducing fluid flow friction loss in pipeline transmission of a hydrocarbon fluid by providing a continuous source of the dissolved polymer.
U.S. Pat. No. 4,016,894 discloses that drag in turbulent aqueous streams may be reduced by a powder composition of a finely divided hygroscopic drag reducing powder, for example, poly(ethylene oxide), and a colloidal size hydrophobic powder, for example, an organosilicon-modified colloidal silica, along with an inert filler such as sodium sulfate. The powder composition is injected into the turbulent stream by first mixing the powder with water to form a slurry and immediately thereafter drawing the slurry through an eductor into a recycle stream between the downstream and upstream ends of a pump for the turbulent stream.
U.S. Pat. No. 4,177,177 describes a polymer emulsification process comprising intimately dispersing a liquified water insoluble polymer phase in an aqueous liquid medium phase containing at least one nonionic, anionic or cationic oil-in-water functioning emulsifying agent. This is done in the presence of a compound selected from hydrocarbons and hydrocarbyl alcohols, ethers, alcohol esters, amines, halides, carboxylic acid esters, and mixtures thereof, which are inert, non-volatile, water insoluble, liquid and contain a terminal aliphatic hydrocarbyl group of at least about 8 carbon atoms. The resulting crude emulsion is subjected to the action of comminuting forces sufficient to enable the production of an aqueous emulsion containing polymer particles averaging less than about 0.5 microns in size.
U.S. Pat. No. 4,263,926 provides a method and apparatus for maintaining polymer particles in readily recoverable, discrete form, and for injecting the particles into a pipeline hydrocarbon by disposing particulate polymer within a storage hopper having a cone bottom and an auger extending upwardly from the bottom. The auger is rotated to cause the polymer particles to revolve in the hopper, reversing the rotation of the auger to pass polymer particles downwardly into a mixing chamber below the hopper. The particles pass through a rotary metering valve, or combination of a bin activator, intermediate storage and rotary metering valve, at the upper end of the chamber, while simultaneously spraying a liquid such as oil or water tangentially in the chamber. The chamber may optionally be agitated and a slurry of particulate polymer and liquid removed therefrom and injected into a pipeline hydrocarbon.
A technique for extremely rapid dissolution or dispersion, essentially on a molecular level, of certain polymeric materials in compatible liquid vehicles is described in U.S. Pat. No. 4,340,076. The polymeric materials are comminuted at cryogenic temperatures and are then introduced into a liquid vehicle, preferably while still at or near cryogenic temperatures. At low concentrations the resulting blend or system displays reduced friction to flow, while high concentrations may be used to immobilize the liquid vehicle and/or to reduce its vapor pressure.
From reviewing the many foregoing prior patents it will be appreciated that considerable resources have been spent on both chemical and physical techniques for easily and effectively delivering drag reducing agents to the fluid that will have its friction reduced. Yet none of these prior methods has proven entirely satisfactory. Thus, it would be desirable to identify a method of size reduction that can be carried out with fewer steps and/or simplified equipment and under non-cryogenic conditions, wherein the resulting particulate DRA is suitable for incorporation into a slurry or dispersion at relatively high polymer concentration levels.